The present invention relates to an improvement of a seal device provided for a linear guide which is used with machine tools, industrial machines, and so forth.
A conventional linear guide of this type, as shown in FIGS. 5 and 6, provides: a guide rail 1 which is laid axially of the linear guide; and a slider 2 substantially U-shaped in section which is movably mounted on the guide rail 1. First ball rolling grooves 3 are formed in both side (right and left) surfaces of the guide rail 1. The slider 2 includes a slider body 2A having right and left wings 4 in the inner surfaces thereof, so that the slider 2 is substantially U-shaped in section by the right and left wings 4. As shown in FIG. 6, second ball rolling grooves 5 are formed so that the second ball rolling grooves 5 are confronted with the above-described first ball rolling grooves 3 when the slider is mounted on the guide rail. A number of balls 6 serving as rolling elements are rollingly set between the first and second ball rolling grooves 3 and 5, so that the slider 2 is axially moved on the guide rail 2 while rolling the balls 6. Ball returning paths 7 are formed in the wings 4 of the slider body 2A, while arcuate paths 8 are formed in two end caps 2B substantially U-shaped in section which are set on the front and rear ends of the slider body 2A, respectively, thus forming endless ball circulating paths.
In each of the ball circulating paths, the balls 6 rolling between the guide rail 1 and the slider 2 are advanced in the path defined by the ball rolling grooves 3 and 5 in the direction of movement of the slider 2 at a speed lower than the speed of the slider 2 to one end portion of the slide body 2A, where they are guided by the arcuate path 8 into the ball returning path 7 while making a U-turn. The balls 6 thus guided are moved along the ball returning path 7 to the other end portion of the slider body 2A, where they are guided by the arcuate path 8 into the path defined by the ball rolling grooves 3 and 5 while making a U-turn in the opposite direction.
In FIG. 5, reference character q designates a grease nipple through which lubricant is supplied to the ball rolling paths in the slider 2. In FIG. 6, reference character H designates holders which prevent the balls 6 from coming off when the slider 2 is disengaged from the guide rail 1.
If foreign matters such as dust and chips enter the gaps between the guide rail 1 and the slider 2 mounted on the guide rail 1 to stick onto the surfaces of the ball rolling grooves, they obstruct the smooth rolling of the balls 6. In order to overcome this difficulty, a pair of side seals 10 and a pair of under seals 11 are mounted on the slider 2. That is, the side seals 10 are set on the front and rear end faces 2c of the slider 2, respectively, to prevent the entrance of foreign matters into the slider through the gaps which are formed between the guide rail 1 and the front and rear end faces of the slider 2 (hereinafter referred to as "side gaps", when applicable). The under seals 11 are mounted on the lower surfaces of the right and left wings 4, respectively, to prevent the entrance of foreign matters into the slider through the gaps which are formed between the lower surfaces of the right and left wings 4 and the right and left side surfaces 1b of the guide rail 1 (hereinafter referred to as "under gaps", when applicable).
Each of the side seals 10 is formed by welding a nitrile or urethane rubber to a steel plate U-shaped in section. The side seals 10 thus formed are fixedly secured to the front and rear end caps 2B of the slider 2 with bolts so that they are in slide contact with the surfaces of the guide rail 1 to prevent the entrance of foreign matters through the side gaps.
Each of the under seals 11 is formed by welding a nitrile or urethan rubber to an elongated steel plate. The under seals 11 thus formed are used as non-contact seals. That is, they are fixedly secured to the lower surfaces of the right and left wings 4 with rivets so that the seal lips of the under seals 11 thus secured are extremely slightly spaced from the right and left side surfaces 1b of the guide rail 1, respectively, to the extent that the entrance of foreign matters through the under gaps is prevented.
In the conventional linear guide, the side seals and the under seals are made of nitrile or urethan rubber which is not of self-lubricating type. Hence, in order to reduce the friction between those seals and the guide rail thereby to minimize the wear of them and to allow the linear guide to smoothly operate, heretofore external lubrication is employed. Therefore, in the case where the linear guide is used under the circumference that cutting oil sprinkles on it, no problems occur with it. However, if it is used under the circumference that foreign matters such as wooden particles and molding powder sprinkle over it, then those foreign matters absorb the lubricant, as a result of which the seals are acceleratively worn out, so that the linear guide becomes unsatisfactory in operation.
Furthermore, in the case of the conventional under seals of the linear guide, in order to reduce the frictional resistance between the right and left side surfaces 1b of the guide rail and the lips of the under seals, there are provided slight gaps between them, or the seal lips lightly touch the right and left side surfaces 1b of the guide rail if they are used as contact seals. Therefore, the under seals thus arranged will not adversely affect the operability of the slider 2; however, they, being low in sealing performance, cannot completely prevent the entrance of small foreign matters such as dust into the slider 2.